This invention relates to RF antenna switches. In particular, this invention relates to relays used as RF antenna switches at frequencies up to 800 MHz.
An RF relay used as an antenna switch is typically a single pole, double throw relay, having the common contact switched between two contacts by an armature. When the armature is in a first position, one switch contact is connected to the common contact. With the armature in the other position, the other switch contact is connected to the common contact. To use a single pole double throw relay as an antenna switch, therefore, the antenna would normally be connected to the common node and the transmitter and receiver connected to the appropriate switch contacts.
During transmit mode, RF energy from the transmitter can leak to the receiver by virtue of stray capacitance existing in the relay. As the reactance of stray capacitance between the receiver and transmitter decreases, and as the frequency of the RF energy increases, the signal leaked to the receiver from the transmitter increases possibly reaching levels sufficient to damage the receiver's components. The level of signal coupled to the receiver from the transmitter in an antenna switch is often expressed in decibels as the isolation loss. The higher the isolation loss of an antenna switch, the greater the isolation of the transmitter signal from the receiver.
Many physical characteristics affect isolation loss in a relay. As the physical size of RF relays used for antenna switches decreases the coupling between a transmitter and a receiver increases, decreasing the isolation loss of the relay. Other factors such as dielectric selection, spacing between the contacts, and configuration of electrodes used to fabricate the relay can also affect isolation loss.
In many circuits, miniaturization is important. Small relays are frequently used to switch transmitters and receivers between the antenna. There are many compact RF relays suitable for printed circuit applications that have relatively high isolation losses. The principal drawback of these prior art RF relays is their cost, as they are substantially more expensive than other types of relays. A low cost relay having improved isolation loss when used at even high frequencies, and that is compact and usable with printed circuit board applications would be an improvement over the prior art.